(a) Field of the Invention
The present invention relates to a zoom lens system, and more particularly, to a zoom lens system which is compact in size while providing exceptional optical performance.
(b) Description of the Related Art
Lens shutter cameras, video cameras, etc. are becoming increasingly smaller, requiring short zoom lens systems.
Zoom lens systems for compact cameras typically include, when viewed from an object, a first lens group with a positive refractive power and a second lens group with a negative refractive power. The magnification of the zoom lens system is varied by changing the distance between the first lens group and the second lens group.
Such zoom lens systems are disclosed in Japanese Publications Nos. Hei 2-190812, Hei 5-134180, Hei 6-130298, Hei 6-281861, Hei 7-120675, and Hei 8-219542, and in U.S. Pat. No. 5,327,290.
The zoom lens system of Japanese Publications No. Hei 2-190812, Hei 6-130298 and Hei 8-21954 have a viewing angle between 53.degree. and 58.degree. and a focal length greater than 39 mm at the wide-angle position. This increases the focal length at a telephoto position, making it difficult to reduce the total length of the zoom lens system.
The zoom lens system of Japanese Publication No. Hei 2-190812 has a first lens group with five lenses and a second lens group with four lenses; the zoom lens systems of Japanese Publications Nos. Hei 2-134180 and Hei 7-120675include a first lens group with five lenses; and the zoom lens system of Japanese Publication No. Hei 6-281861 includes an aperture positioned inside of a first lens group.
In the above mentioned zoom lens systems, the lens groups are divided into forward and rear lens groups based on their position relative to the aperture. The lens groups are simultaneously moved to adjust the focus while the aperture remains stationary. Accordingly, this operation of the lens system is complicated and difficult to control, and the complexity of the mechanism increases the overall manufacturing costs.
Also, such zoom lens systems have a telephoto ratio of 0.9, making it difficult to reduce the total length of the system.